Food habit and ecological balance of fish species in Osun river, Nigeria

The food habit and ecological balance of fish species in Osun River were investigated for a period of 12 months (November 2017 to October 2018) with monthly sampling of water and fish species in the river. Fish were sampled using monofilament gill nets of mesh size between 25mm and 101mm. A total of 4544 individuals belonging to 19 species and 10 families were captured. They were grouped based on their feeding habits into herbivores, carnivores, and omnivores. Carnivores dominated the River (38.63%) with Cichlids being the most abundant family (95.10%) and Oreochromis niloticus the most abundant fish species (14.10%). The Forage - Carnivore ratio (F/C) for the dry, wet and combined season was 0.64, 0.34 and 0.48 respectively. T-test showed significant differences (P < 0.05) between all the trophic groupings in relation to seasons. The mean values recorded across the sampling months were Temperature (18.70 oC ± 2.69), pH (7.10 ± 0.25) and Dissolved Oxygen (3.20 mg/L ± 0.54) while Ammonia (1.20 mg/L ± 0.18) was significantly different (P < 0.05) across the months of study. For the sampling points, mean values recorded were Temperature (17.90 oC ± 0.31), pH (7.20 ± 0.12), Dissolved Oxygen (3.20 mg/L ± 0.27 mg/L) and Ammonia (0.10 mg/L ± 0.21). The abundance of carnivores is not desirable, and it is therefore essential to maintain the ratio of forage and carnivorous fish species in the river for conservation of fish species.